One of the new features in iOS 8 is the ability to for developers to add share extensions to their apps that can be used in other apps. As the name suggests, share extensions in iOS 8 allow you to share a picture, document or other file with another app that is installed on your iPhone or iPad. You have seen this already in iOS 7 and iOS 8 with the ability to share with Twitter, Facebook and other apps that you have installed. Now in iOS 8 you can control which apps you want to share content with to make it a more personalised and productive experience.
In order for you to be able to add share extensions in iOS 8 the app you want to share with must have the ability to take advantage of this feature. Not all apps do but you will be able to quickly determine if it does when you go through this How To. While my screen captures are for iPhone, this functionality works the same on your iPad or iPod Touch running iOS 8